This invention relates to a multiple message frame adaptor apparatus for loop communication systems and particularly to such an adaptor for selective connection of a single message frame originating device into the system.
Digital loop communication systems are advantageously employed in the monitoring and transmission of data and other information between a central controller and remote stations. A very satisfactory loop system is disclosed in U.S. Pat. No. 3,845,472 wherein a computer programmed loop controller is operable to generate multiple bit message frames in timed spaced sequence, with the frames serially passed through a plurality of remote stations. Each of the remote stations includes a message processing unit which includes suitable frame handling logic for continuously detecting the status of each of the message frame bits and, if appropriate, providing communication at such remote stations and retransmitting of the message frame either modified or unmodified to the next downstream station.
In certain applications generally identified as life safety type systems which may provide for fire detection, burglary alarm systems and the like, a single loop system may not provide the level of security required or desired. A short or open fault in the transmission loop will terminate communication. Although such fault conditions can be readily identified, as disclosed in the above-mentioned patent, alarm conditions arising during the failure of the transmission path would go undetected and thereby present a potentially hazardous situation. The copending application of Strojny et al entitled "DATA COMMUNICATIONS SYSTEMS EMPLOYING REDUNDANT SERIES TRANSMISSION LOOPS" Ser. No. 598,376 filed on the same day as this application and assigned to the same assignee, discloses a redundant transmission path system with increased reliability and security of transmission. As more fully discloses therein, the several remote stations are interconnected to each other and to message frame sources through primary and secondary transmission paths or trunks. The primary trunk is normally connected to the frame processing means. A monitoring means detects failure thereof to automatically and directly connect the secondary trunk at that station to the frame processing means. Dual transmission means, of course, require a dual message frame source to provide for the appropriate generation of the dual frames for transmission over the pair of trunks and must be able to terminate the two received completely processed messages. Further, the dual loop system disclosed does not protect against a fault in the controller station. Thus, if the controller should malfunction, the total data communication would be inactive.
An extremely high security application of the loop system may further require the use of a backup message frame source with or without the redundancy in a loop control system. Thus, if a central controller or a message source terminates, all loop communication, of course, terminates in either a single or dual transmission system. The safety life system may be desirably provided with a primary loop controller in combination with a secondary or backup loop controller with means for automatic interconnecting of the secondary unit into the system in response to failure of the primary controller. Further, many data loop systems only require the single transmission loop and the conventional redundant system may require significantly different constructions, with attendant initial manufacturing complexities and costs.